Xylitol is a naturally occurring five-carbon sugar alcohol present in many fruits and vegetables and produced in the human body during normal metabolism. Xylitol is also an important industrial product and is widely used in the production of confectionary products, including sugarless chewing gum, breath mints and dry hard candies, as well as in dental care products, health promoting products, pharmaceutical products and the like.
Certain characteristics of xylitol make it an attractive sweetener or sugar substitute in various contexts, particularly in the production of sweetened food products. For example, xylitol is non-toxic and has approximately the same sweetness as sucrose with a lower caloric content of about 2.4 kcal/g. Xylitol is metabolised independently of glucose and can be safely consumed by non-insulin dependent diabetics, has a very low glycemic index, and is reported to have an anti-ketogenic effect in diabetes. Xylitol crystals have an endothermic heat of solution and produce a cool feeling when dissolved in the mouth. Xylitol is also believed to be cariostatic and even anti-cariogenic, and is believed to not be utilized by the microflora of the mouth that produce plaques. Indeed, the use of xylitol in place of sucrose has been linked to a reduction in dental carries. Overall, xylitol is a desirable sweetener.
Xylitol is usually prepared by processes utilizing various natural raw materials, especially xylan-containing materials. Xylitol may be obtained by a variety of processes, including the hydrogenation of xylose that is isolated from a hemicellulose (xylan or arabinoxylan) hydrolyzate, as disclosed in U.S. Pat. Nos. 2,989,569, 3,558,725, and 4,008,285.
Catalytic hydrogenation of D-xylose in hemicellulose hydrolyzates remains the primary industrial source of xylitol. Industrial production of D-xylose is primarily performed by hydrolysis of hemicellulose (xylans and arabinoxylans). However, many of these processes for the production of xylitol are expensive or time-consuming, and a variety of alternative xylitol synthesis methods have been proposed. These include various synthetic chemical processes, the use of microorganisms, and processes such as fermentation. However, despite these developments, a need exists to produce xylitol in a manner that is low cost and yields high-purity product. A decrease in the waste produced during its production is also desirable. In view of the increasing use of xylitol, in particular due to its properties as sweetener and therapeutic effects, there is a continuing need for methods for the production of xylitol.